AfcT OE MAKING G t N-FLTNTS. f 91 



The workmen felect the (lones proper for their ufe by Sele&ion of the 

 -i • 110 r™ A i A c a\. beft flints trom 



their external character. 1 hey compare that part ot the their greaf 



mafles of filex, which is uniformly femi-tranfparent and co-afped. 



loured, to the inner ikin of bacon, which they call couenne. 



They (ay that one flint has more or lefs couenne, or is more or 



lefs fat than another. They affert that the upper part of a 



Hint is always of a better quality than the lower. Flints are 



confidered as imperfect or intractable when naturally deprived 



of any of the external characters before indicated, or when 



injured by long expofure to the air. Moft of the manes are 



fubject to have whitifh opaque fpots and a kind of knots 



where the material is harder than in the other part of the 



ftone. When thefe accidents are too abundant, the ftone is 



rejected as ufelefs. 



The phyfical characters are as follow : -^Specific gravity of Phyfical charac- 



the white filex pyromachus from the banks of the Cher tcrs *. Sp l eci ? c 

 f J gravity, hard- 



proved to be 26041 ; that of the blackifh kind from the chalk ntfs, brittlenefs," 

 ifles of Laroche Guion was 25954. In this refpect it does &c# 

 not differ eflentially from the other varieties of filex, of which 

 the fpecifie gravities are ufually between 26100 and 25900. 

 Hardnefs a little fuperior to that of jafper, but inferior to that 

 of agate and chalcedony. It is nearly the fame as that of 

 the other common flints. Brittlenefs. It is more brittle than 

 moft other iiliceous fiones. The light coloured is more fo 

 than the darker ; thefe laft being rather more fcintillant, and 

 and wear away the hammer more quickly. When two 

 pieces of the filex pyromachus are ftrongly rubbed together, 

 triey emit the peculiar well known fmell of flliceous fiones, 

 but in this variety it is more ftrong than in any other. 

 Chemical characters. Action of the air. 



The filex pyromachus, deprived of its natural coating, and Chemical cha- 

 expofed for a long time to the changes of the atmofphere, ac- r *^rs. Action 

 quires a lecond white friable coating, confifting of the filex 

 reduced to powder • and even its internal part lofes its greafy 

 appearance and femi-traniparency, fo as to become whitifli. 

 In this cafe the fpecitic gravity, which was 25954, becomes 

 25754, coniequently it has loll 200 parts of the weight it 

 poffefled at firft. 



The fitcx pyromachus is fometimes too moift when taken It contain* 

 Out of the quarry. It requires to be dried ; but if by too long moifture. 

 expofure to the air or the v. aid it lotos a certain portion of 



humidity 



